Contrasting effects of mangroves and armoured shorelines on fish assemblages in tropical estuarine seascapes

Coastal seascapesare composed of a diversity of habitatsthat are linked in space and time by the movement of organisms. The context and configuration of coastal ecosystems shapes many important properties of animal assemblages, but potential seascapeeffects of natural and artificial habitatson nearby habitatsare typically considered in isolation. We test whether, and how, the seascapecontext of natural and urban habitatsmodified fish assemblages across estuaries. Fish were sampled with underwater videos in five habitattypes ( mangroves, rock bars, log snags, unvegetated sediments, armouredshorelines) in 17 estuariesin eastern Australia. Different habitatssupported distinct fish assemblages, but the spatial context of mangrovesand armouredshorelines had pervasive ecological effects that extended across entire estuaries. In most estuarine habitats, fish diversity and abundance was greatest when they were in close proximity of mangroves, and decreased due to the proximity of armouredshorelines. Many cities are centred on estuaries, and urban expansion is often associated with the fragmentation of mangroveforests. Our findings emphasize that these transformations of urban estuarine landscapes are likely to propagate to broader ecological impacts detectable in multiple habitatsbeyond mangroveforests.